What are the classifications of myasthenia gravis (MG)?

Updated: Aug 27, 2018
  • Author: Abbas Jowkar, MD; Chief Editor: Nicholas Lorenzo, MD, MHA, CPE  more...
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Answer

In May 1997, the Medical Scientific Advisory Board (MSAB) of the Myasthenia Gravis Foundation of America (MGFA) formed a task force to address the need for universally accepted classifications, grading systems, and analytic methods for management of patients undergoing therapy and for use in therapeutic research trials. As a result, the MGFA Clinical Classification was created. [3] This classification divides MG into 5 main classes and several subclasses, as follows.

  • Class I: Any ocular muscle weakness; may have weakness of eye closure. All other muscle strength is normal.
  • Class II: Mild weakness affecting other than ocular muscles; may also have ocular muscle weakness of any severity.
    • Class IIa: Predominantly affecting limb, axial muscles, or both. May also have lesser involvement of oropharyngeal muscles.
    • Class IIb: Predominantly affecting oropharyngeal, respiratory muscles, or both. May also have lesser or equal involvement of limb, axial muscles, or both.
  • Class III: Moderate weakness affecting other than ocular muscle; may also have ocular muscle weakness of any severity
    • Class IIIa: Predominantly affecting limb, axial muscles, or both. May also have lesser involvement of oropharyngeal muscles.
    • Class IIIb MG: Predominantly affecting oropharyngeal, respiratory muscles, or both. May also have lesser or equal involvement of limb, axial muscles, or both.
  • Class IV: Severe weakness affecting other than ocular muscles; may also have ocular muscle weakness of any severity.
    • Class IVa: Predominantly affecting limb, axial muscles, or both. May also have lesser involvement of oropharyngeal muscles.
    • Class IVb: Predominantly affecting oropharyngeal, respiratory muscles, or both. May also have lesser or equal involvement of limb, axial muscles, or both.
  • Class V: Defined by intubation, with or without mechanical ventilation, except when used during routine postoperative management. Use of a feeding tube without intubation places the patient in class IVb.

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